---
title: sort-heritage-clauses
description: Enforce sorting of heritage clauses for improved readability and maintainability. Use this ESLint rule to keep your heritage clauses well-organized
shortDescription: Enforce sorted heritage clauses
keywords:
  - eslint
  - sort heritage clauses
  - sort implements
  - sort extends
  - eslint rule
  - coding standards
  - code quality
  - javascript linting
  - typescript heritage clauses sorting
---

import CodeExample from '../../components/CodeExample.svelte'
import Important from '../../components/Important.astro'
import CodeTabs from '../../components/CodeTabs.svelte'
import dedent from 'dedent'

Enforce sorted heritage clauses.

This rule detects instances where heritage clauses are not sorted and raises linting errors, encouraging developers to arrange elements in the desired order.

## Try it out

<CodeExample
  alphabetical={dedent`
    interface Interface extends Logged, Pausable, StartupService {
     // ...
    }

    class Class implements Logged, Pausable, StartupService {
     // ...
    }
  `}
  lineLength={dedent`
    interface Interface extends StartupService, Pausable, Logged {
     // ...
    }

    class Class implements StartupService, Pausable, Logged {
     // ...
    }
  `}
  initial={dedent`
    interface Interface extends StartupService, Logged, Pausable {
     // ...
    }

    class Class implements StartupService, Logged, Pausable {
     // ...
    }
  `}
  client:load
  lang="tsx"
/>

## Options

This rule accepts an options object with the following properties:

### type

<sub>default: `'alphabetical'`</sub>

Specifies the sorting method.

- `'alphabetical'` — Sort items alphabetically (e.g., “a” < “b” < “c”) using [localeCompare](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare).
- `'natural'` — Sort items in a [natural](https://github.com/yobacca/natural-orderby) order (e.g., “item2” < “item10”).
- `'line-length'` — Sort items by code line length (shorter lines first).
- `'custom'` — Sort items using the alphabet specified in the [`alphabet`](#alphabet) option.
- `'unsorted'` — Do not sort items. [`grouping`](#groups) is still enforced.

### order

<sub>default: `'asc'`</sub>

Specifies whether to sort items in ascending or descending order.

- `'asc'` — Sort items in ascending order (A to Z, 1 to 9).
- `'desc'` — Sort items in descending order (Z to A, 9 to 1).

### fallbackSort

<sub>
  type:
  ```ts
  {
    type: 'alphabetical' | 'natural' | 'line-length' | 'custom' | 'unsorted'
    order?: 'asc' | 'desc'
  }
  ```
</sub>
<sub>default: `{ type: 'unsorted' }`</sub>

Specifies fallback sort options for elements that are equal according to the primary sort
[`type`](#type).

Example: enforce alphabetical sort between two elements with the same length.
```ts
{
  type: 'line-length',
  order: 'desc',
  fallbackSort: { type: 'alphabetical', order: 'asc' }
}
```

### alphabet

<sub>default: `''`</sub>

Used only when the [`type`](#type) option is set to `'custom'`. Specifies the custom alphabet for sorting.

Use the `Alphabet` utility class from `eslint-plugin-perfectionist/alphabet` to quickly generate a custom alphabet.

Example: `0123456789abcdef...`

### ignoreCase

<sub>default: `true`</sub>

Specifies whether sorting should be case-sensitive.

- `true` — Ignore case when sorting alphabetically or naturally (e.g., “A” and “a” are the same).
- `false` — Consider case when sorting (e.g., “a” comes before “A”).

### specialCharacters

<sub>default: `keep`</sub>

Specifies whether to trim, remove, or keep special characters before sorting.

- `'keep'` — Keep special characters when sorting (e.g., “_a” comes before “a”).
- `'trim'` — Trim special characters when sorting alphabetically or naturally (e.g., “_a” and “a” are the same).
- `'remove'` — Remove special characters when sorting (e.g., “/a/b” and “ab” are the same).

### locales

<sub>default: `'en-US'`</sub>

Specifies the sorting locales. Refer To [String.prototype.localeCompare() - locales](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare#locales).

- `string` — A BCP 47 language tag (e.g. `'en'`, `'en-US'`, `'zh-CN'`).
- `string[]` — An array of BCP 47 language tags.

### groups

<sub>
  type: `Array<string | string[]>`
</sub>
<sub>default: `[]`</sub>

Specifies a list of heritage clause groups for sorting.

Predefined groups:

- `'unknown'` — Heritage Clauses that don’t fit into any group specified in the `groups` option.

If the `unknown` group is not specified in the `groups` option, it will automatically be added to the end of the list.

Each heritage clause will be assigned a single group specified in the `groups` option (or the `unknown` group if no match is found).
The order of items in the `groups` option determines how groups are ordered.

Within a given group, members will be sorted according to the `type`, `order`, `ignoreCase`, etc. options.

Individual groups can be combined together by placing them in an array. The order of groups in that array does not matter.
All members of the groups in the array will be sorted together as if they were part of a single group.

### customGroups

<sub>
  type: `{ [groupName: string]: string | string[] }`
</sub>
<sub>default: `{}`</sub>

You can define your own groups and use regex to match specific heritage clauses.

Each key of `customGroups` represents a group name which you can then use in the `groups` option. The value for each key can either be of type:
- `string` — A heritage clause's name matching the value will be marked as part of the group referenced by the key.
- `string[]` — A heritage clause's name matching any of the values of the array will be marked as part of the group referenced by the key.
The order of values in the array does not matter.

Custom group matching takes precedence over predefined group matching.

#### Example

Put the `WithId` clause before anything else:

```ts
interface Interface extends WithId, Logged, StartupService {
 // ...
}
```

`groups` and `customGroups` configuration:

```js
 {
   groups: [
     'withIdInterface',         // [!code ++]
     'unknown'
   ],
+  customGroups: {              // [!code ++]
+    withIdInterface: '^WithId' // [!code ++]
+  }                            // [!code ++]
 }
```

## Usage

<CodeTabs
  code={[
    {
      source: dedent`
        // eslint.config.js
        import perfectionist from 'eslint-plugin-perfectionist'

        export default [
          {
            plugins: {
              perfectionist,
            },
            rules: {
              'perfectionist/sort-heritage-clauses': [
                'error',
                {
                  type: 'alphabetical',
                  order: 'asc',
                  fallbackSort: { type: 'unsorted' },
                  ignoreCase: true,
                  specialCharacters: 'keep',
                  groups: [],
                  customGroups: {}
                },
              ],
            },
          },
        ]
      `,
      name: 'Flat Config',
      value: 'flat',
    },
    {
      source: dedent`
        // .eslintrc.js
        module.exports = {
          plugins: [
            'perfectionist',
          ],
          rules: {
            'perfectionist/sort-heritage-clauses': [
              'error',
              {
                type: 'alphabetical',
                order: 'asc',
                fallbackSort: { type: 'unsorted' },
                ignoreCase: true,
                specialCharacters: 'keep',
                groups: [],
                customGroups: {}
              },
            ],
          },
        }
      `,
      name: 'Legacy Config',
      value: 'legacy',
    },
  ]}
  type="config-type"
  client:load
  lang="tsx"
/>

## Version

This rule was introduced in [v4.0.0](https://github.com/azat-io/eslint-plugin-perfectionist/releases/tag/v4.0.0).

## Resources

- [Rule source](https://github.com/azat-io/eslint-plugin-perfectionist/blob/main/rules/sort-heritage-clauses.ts)
- [Test source](https://github.com/azat-io/eslint-plugin-perfectionist/blob/main/test/sort-heritage-clauses.test.ts)
